"My mom is going to kill me." A phrase used so often it has lost its urgency and true meaning.

But the Casey Anthony trial commanded our attention because it tapped into this dark side of motherhood. Our society promotes and embraces an ideal in which being a mom is a fun, beautiful, spiritual experience. Having a child is supposed to be a blissful highlight in a woman's life; the word "mothering" is synonymous with "nurturing." But in the back of our minds, we know the truth: From post-partum depression to infanticidal urges, mothers throughout history have also been reluctant, exasperated, resentful…and murderous.

Infanticide is a global phenomenon, and in many ancient cultures, it was not only permissible, but routine. (In the animal kingdom, it continues to be incredibly common.) Today, while all kinds of crimes are considered horrendous and unfathomable, women accused of killing their children earn major headlines. Captivate us.

In 1995, Susan Smith was convicted of murdering her two sons by strapping them into their car seats and letting the vehicle roll into a lake. She landed the cover of Time magazine, and three books about her life have been published. Andrea Yates drowned her five kids in the bathtub of her house in 2001. Her story inspired a Desperate Housewives storyline, a Law & Order episode, and a feature film called Baby Blues. Diane Downs shot her three children in 1983, and became the subject of a book and a made-for-TV movie. Earlier this year in New York, 25-year-old Lashanda Armstrong drove herself and her four children into the Hudson River (one son survived). China Arnold killed her infant daughter by placing her in a microwave, as did 29-year-old Ka Yang. Each story is horrific it its own way, and we think of these crimes as incredibly taboo — it's one thing to harm a stranger, but an innocent child? Your own flesh and blood?

But in some way, doesn't the fact that a child is a mother's "own flesh and blood" mean that a primal part of us, as humans, understands the act of killing a child? Because if a child is made of your own flesh, then it is a part of you. An extension of yourself. Under your control. Operating under your agency, existing because you created it, and therefore yours to govern, manipulate, command, discipline, punish — and destroy.

The ancient Greek play Medea revolves around a woman betrayed by her husband, Jason. He's cruelly taken up with a new woman, and to get back at him, Medea (pictured above in an 1838 painting by Eugène Delacroix, which hangs in the Louvre) decides to kill the two sons she and Jason had together. In a monologue, Medea explains:

"This shall not be, nor will I ever leave
my sons to be insulted by their foes.
They certainly must die; since then they must,
I bore and I will slay them: 'tis a deed
resolved on, nor my purpose will I change."

A similar sentiment was spoken by Cliff Huxtable on The Cosby Show:

"I brought you in this world, and I can take you out."

It's as though we secretly believe that, since a child is made from a mother's energy, her very blood, sweat and tears, she has the right to cultivate — or assassinate — her creation.

Once when I was young, in the midst of moving, my family discovered that one of my sister's pet rabbits was pregnant. Moving upset the bunny greatly — she'd built a nest in her cage, but when it was moved, she no longer wanted to sleep in the little mound of newspaper she'd created. When the blind, hairless baby bunnies were born, the rabbit did not care for them properly. Some died. Some she killed. Animals eat their young sometimes, we said to each other, crying and sick about what had happened but also convinced, somehow, that the mother bunny knew best.

Folks certainly love to tsk-tsk a neglectful, apathetic mom. But the real reason Anthony's case was national news for months? In imagining that Anthony was guilty, we were forced to remember that a mother is not always the smiling benevolent caricature cleaning and baking in commercials. Pushing a child out of your vagina does not turn you into a saint. A mother can be ruthless, depressive, vindictive. And despite being pigeon-holed as a nurturer, a mother can be a murderer. It happens more often than we like to admit.